Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains generally to devices and methods for interfacing, interconnecting and assembling a network of individual MEMS modules (i.e. microfluidic pumps and valves, miniature reaction chambers, optical detection schemes, CMOS control circuitry, etc.) for creating integrated miniature instruments, and more particularly to miniature devices and methods for constructing those devices in a microscopic environment which allows the manufacture of miniature high precision devices such as fiber optic switches, xyz translational optical benches and other devices on a microscopic scale.
2. Description of the Background Art
Microfabrication is a generic term for a rather large, eclectic, and sophisticated collection of different processing techniques. It is both a powerful and versatile technology which enjoys a well respected history in the fabrication of high density, high precision integrated electronics, LED""s, solid state lasers, and optical detectors. The recent explosion in the field of optical communications, imaging, optical signal processing, and optical recording has fueled a focused search for reliable, compact, inexpensive, and low loss ancillary micro-accessories to augment functionality in expanding optical Microsystems. Foremost in the search for micro-accessories has been the application of surface micromachining to the fabrication of optical and mechanical microcomponents.
Surface micromachining was introduced in the late 1960s as a technology for the generation of elegant and moveable micromechanical components such as micro-gears, tongs, cams, and including a micromotor the diameter of a human hair. However, surface micromachining is inherently limited in its application because it provides only a limited range of motion for the mechanical components (a few hundred micrometers at best) as well as a particularly planar geometry which does not lend itself to three dimensional device construction. For example, fiber optic communication lines are approximately 125 micrometers in diameter, and therefore, physical fiber optic switches can require much more than microns of translation to effect switching between fiber optic lines.
Furthermore, systems integration of microfabricated components has recently blossomed into a critically emerging field of interest in today""s microfabrication environment. Already, a literal zoo of revolutionary microdevices has appeared in the literature, generating such futuristic speculations as nano-robots and micro flying machines. Toyota has even fabricated a microcar powered by magnetic induction and Seiko has demonstrated a microlathe capable of turning a 40 micrometer needle tip. Although such interesting creations entice the imagination, practical Microsystems have yet to realize their full commercial potential, due mostly to stubborn technical limitations in present microfabrication technologies and techniques.
Despite the plethora of micromachined components reported in the literature to date, micromachines in general have recently come under strong criticism for promising much but delivering little. Generally, there is a growing sentiment that micromachining is more of an esoteric laboratory curiosity than a practical commercial commodity. For this reason, commercial and industrial concerns are backing off their initial excitement with the microworld and concentrating on more immediate products.
At least a portion of micromachining""s perceived lackluster performance in microelectromechanical systems (MEMS) stems from a genuine limitation in the way the technology has developed. As it stands today, micromachining is a rather diverse collection of disjointed and inherently incompatible techniques. Although each particular micromachining technique is ideally suited to fabricate certain, very specific, types of microdevices, no one technology is capable of optimally fabricating all microstructures, nor can different micromachining techniques be xe2x80x98mixed and matchedxe2x80x99 to fill in the missing components. Once a basic fabrication process is started, fundamental process incompatibilities dictate that it cannot be altered despite the fact that some of the required components may best be fabricated by other means. This translates into less than optimal performance for even the simplest microdevice, and a complete disaster for complex Microsystems requiring a broad spectrum of interconnected microdevices. For this reason the most successful micromachined devices on the market today are relatively simple straightforward projects focusing on one specific micromachining technique.
The problem is best illustrated by the recent attempts to create integrated free-space microphotonics systems: the so-called optical bench on a chip. Up to now, development of micro-optical systems has been divided between monolithic guided-wave approach, in which passive and/or electro-optic control networks route optical beams through planar waveguides and free-space microphotonic systems. Although the waveguide approach has enjoyed a modest degree of success, the method is rather limited in scope and potential application. Optical benches are now considerably more versatile, but require mechanical components to steer, align, scan, or otherwise manipulate optical beams. In the past, surface micromachining processes were the most widely used for construction of optical and mechanical microcomponents.
Ironically, integration, a touted advantage of surface micromachining, has also been a major impediment in its successful commercialization. Although surface micromachining is an extremely elegant method for the monolithic integration of many micro-opto-mechanical components, unless all necessary components in a microsystem are microfabricated with a virtual 100% yield, integration loses much, if not all, of its appeal. Unfortunately, surface micromachining""s spectrum of available microstructures is insufficient to complete a truly functional microsystem. Input/output has been particularly troublesome for surface-micromachined optics and MEMS in general.
For example, most reports on surface-micromachined integrated optical systems usually show the optical source, III-V laser or LED, xe2x80x9chand gluedxe2x80x9d to an otherwise integrated silicon chip, the reason being that III-V semiconductor processing is inherently incompatible with silicon surface micromachining. Such crude and inaccurate hand assembly/alignment does little justice to the elegant precision available to micromachining.
A significant problem in the microfabrication of complicated systems is that different system components are process incompatible, i.e. the fabrication of one device destroys or impedes the fabrication of another critical component. Therefore, it is advantageous to microfabricate each component separately, using proven techniques and processes best suited for each component, then assemble them in the end to form the completed microsystem. This is a module, or hybrid, approach, and eliminates the issue of process incompatibility. However, to accomplish this, a means to interconnect modules and/or components is required.
Although each micromachining technology by itself may be limited in its range of performance, all micromachining technologies, when considered as a collective unit, generally span the entire spectrum of requisite microdevices. What is desperately needed to make commercially viable microsystems is a unifying micromachining technology which marries this already existing, but rather eclectic, collection of microdevices and micromachining technologies. The concept is not unlike the complimentary synergism between hybrid and integrated electronics, i.e., even though integrated electronic circuits are fast, powerful, and small, without the means to interconnect them to each other, discrete components, and the external world through the use of PC boards, thick-film technology, etc., they are completely useless. As it stands today, micromachining lacks an analogous cohesive inter-connect technology, making any concerted leap into micro-systems xe2x80x9cdifficultxe2x80x9d at best.
The present invention, which will be referred to herein as xe2x80x9cMicroJoineryxe2x80x9d, pertains to a wafer level interconnecting mechanism for assembling and packaging multiple MEMS devices (modules). This new technology allows for both integrating and packaging multiple MEMS modules to form miniature systems and devices. The present invention provides a method for the interconnection and/or assembly of microcomponents to facilitate the conduction of fluidic, electrical and optical signals from one module to another, thereby allowing the assembly of several modules to produce a total microsystem. This technology allows the performance of each component, and the yield of an entire system, to be maximized, translating to a low, per unit, cost.
The present invention generally comprises a novel wafer level interconnecting mechanism for assembling and packaging multiple miniature devices (modules). The joining structures will facilitate the modular placement and self-alignment of each module to each other, or on a single substrate, by locking them into position, thereby significantly simplifying the manufacturing process. The nature of these MicroJoinery structures also allows each module to be logically interchanged to alter the operation and/or function of an entire unit.
MicroJoinery is a hybrid technology which successfully addresses the interface between the many diverse and sometimes mutually exclusive micro-machining techniques. Although this approach appears problematic at first, MicroJoinery makes it a tangible reality and is quickly developing into an indispensable technology that binds all micromachining techniques into a single cohesive unit: bulk micromachining, surface micromachining, LIGA, etc. By using MicroJoinery, discrete microcomponents may be fabricated separately using the micromachining technology most optimal for the function of that particular component and later assembled, interfaced, and/or otherwise aligned within a microsystem in a completely hybrid fashion. This critical feature of MicroJoinery relieves much of the growing pressure to xe2x80x9cintegrate fullyxe2x80x9d an unreasonable expectation to begin with, and provides the necessary technical base to launch MEMS into a practical commercial reality.
By way of example, and not of limitation, the invention generally comprises microfabricated, interlocking, mechanical joints to interconnect different modules and to create miniature devices, as well as a method for fabricating those joints. The invention further comprises a method for the fabrication of MicroJoints in the form of dovetail joints, dado joints, rotary joints, lock and finger joints, and the like, which are then used in the assembly of various microsystems. The joints are micromachined using standard, non standard, and new microfabrication techniques. Various devices can be fabricated using these joints, including fiber-optic switches, xyz translational stages, push-n-lock locking mechanisms, slide-n-lock locking mechanisms, t-locking joints, fluidic interconnects, on/off valves, optical fiber couplers with xy adjustments, specimen holders, and membrane stops. Several of the these devices are fabricated with interlocking xe2x80x9cdovetailxe2x80x9d and xe2x80x9cdadoxe2x80x9d joints. For example, an xyz translational stage could incorporate interlocking xe2x80x9cdovetailxe2x80x9d joints and a xe2x80x9cdadoxe2x80x9d joint for mounting a vertical mirror. The dimensions of the device can be as small as several ten""s of microns or as large as many centimeters.
The joints can be created through various techniques, including microsawing and micromilling, although a preferred method is anisotropic etching. Furthermore, many different materials can be used, such as Ge, GaAs, quartz, etc., but (100) oriented silicon is particularly well suited to creating dovetail joints through an anisotropic etching process. Starting with bare (100) silicon wafers, an etch masking material such as LPCVD silicon nitride, silicon dioxide, or other suitable masking materials is deposited and appropriately patterned using conventional photolithography and chemical etching techniques to expose the underlying silicon. The patterned wafer is then placed in an anisotropic silicon etchant such as KOH, and etched to the designed depth. After the desired depth is reached, the etched wafer is bonded to a virgin silicon wafer using standard silicon wafer bonding techniques. A passivation layer is then deposited over the bonded wafer. The wafer is then mechanically polished or etched to thin it and expose the dovetail joints. At this point the dovetail structures are complete and the wafer is diced using a conventional wafer dicing saw in such a way to have both the xe2x80x9cnegativexe2x80x9d and xe2x80x9cpositivexe2x80x9d dovetail structures, although individual pieces could be fabricated on separate wafers. After dicing, the opposite pieces can be joined by sliding them into each other.
Dado joints can be fabricated from the anisotropic etching of (110) or off axis etching of (100) silicon, by cutting the material using a conventional dicing saws, by micromilling or any combination of these or other techniques. Dado joints are particularly well adapted for bonding portions of material at a perpendicular orientation. Rabbet joints are a slight variation of the dado joint, and may also be fabricated using similar techniques.
Borrowing from woodworking nomenclature, any number of other joints in addition to dovetail, dado and rabbet joints may be recruited into the microlevel including: lock joints, finger joints, mortise and tenon joints, etc. These MicroJoints can be used to create and assemble virtually any desired microsystem through a number of conventional and non conventional methods available to microfabrication including: wafer sawing, micromilling, electrical discharge, electrochemical depositions/etching, molding, LIGA or LIGA-like processes, thick film processes, surface micromachining, wafer bonding methods, or others.
An object of the invention is to provide a method for fabricating integrated miniature instruments capable of much larger gross movements than that afforded by past surface micromachining processes.
Another object of the invention is to provide a means for constructing viable optical switches and couplers capable of handling multiple inputs and outputs.
Another object of this invention is to provide a means for constructing miniature xyz translational optical benches.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.